Typically, a known turbocharger utilizes exhaust-gas energy discharged from an engine and supplies pressurized air into an intake manifold to improve an output. If such a turbocharger is mounted to a vehicle in particular, weight reduction would be required to meet the recent need to improve fuel consumption, and heat-capacity reduction would also be required to suppress a decrease in a temperature of exhaust gas supplied to a downstream catalyst, and thus sheet-metal turbine housings are increasingly used instead of typical cast turbine housings.
Such a turbine housing has a function to take in exhaust gas of an engine and to utilize the exhaust gas to rotate a turbine wheel, and thus an inlet section of the turbine housing is heated by exhaust gas having a temperature of approximately 900° C. to 1000° C. An outlet section of the turbine housing is heated by exhaust gas having a temperature of approximately 700° C., which is reduced due to a decrease in energy from work to rotate the turbine wheel when exhaust gas flows through the turbine wheel. Accordingly, a turbine housing is a component subject to a great temperature difference, and thus to a great thermal-deformation difference between sections due to the temperature difference.
In such a turbine housing with a great thermal-deformation difference between sections, a temperature difference between an exhaust-gas inlet duct part connecting a duct disposed on an inlet of the turbine housing and an inlet area of the turbine housing connected to the exhaust-gas inlet duct part creates a thermal-deformation difference, which generates a thermal-expansion constraint force and compression thermal stress. If thermal stress is repeatedly applied, a damage such as a crack may occur in the turbine housing connected to the exhaust-gas inlet duct part.
Meanwhile, Patent Documents 1 and 2 propose a sheet-metal turbine housing structure, which is a related art.